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Unformatted text preview: e any
ight of evidence
describe the probability of each is issued inNeurons
cess actuevidence is sampled. If, for example, there is an equal
Sensory SignalsTuring’s Weight of Evidence
th
f 1/10 of
prior probability of either hypothesis (which was the
onsidered
eant that
1968; Link and Heath, 1975; Luce, 1986;the weight of
assumption made in Banburismus), then Ratcliff and
ce that is
, implied
Rouder, 1998;equal to the logarithm of the ratio of the
evidence is Stone, 1960; Usher and McClelland, 2001;
od, Howposterior probabilities. In this case, for a given weight
er. 1979).
Vickers, 1979).
df the co“natural
of evidence (e.g., is analogous to in Banburismus):
This problem the stopping point onedimensional
ted quanlar tradeBrownian motion to a pair of barriers (Link, 1992; Ratcliff
Pr(h1m)
obabilities
articular
and Rouder, 1998). The weight of evidence B
means of the normal distribu(3)
log
Pr(h0mdrift rates, (where the subscript i
)
surprisal”
r can be
tions represent the
i
bans but
f reward
reflects B is particular motion strength).the barrier height
the a constant that represents The psychometwhere
m of base
ric function describing the probability of correctly reachin favor of h1. For two mutually exclusive hypotheses
Decision Model
tiontime Figure 2. ing eitherh the is“up” r(h difference between equivalently, given) antineuron is:
or “down” barrier on a Pr(h trial
The weight (Pr(h favor of
evidence in m) over h
the accumulated m) or, responses of a neuron that prefers h and an
1
1
0 7). The curves depicted P computed under the condition that h is true. The thin, wavy line depicts a simulated
1
0
ihich the trajectory that represents how the weight of evidence are grow on a single trial as a function of time. The dashed line depicts the expectation
lities has that prefers h (see Equation
and assuming the of proportionality of relate the accumulated is exPr(h1)), at each time point. Notemightchanging the constantweight used to evidence difference
(mean value) of this trajectory
100 years to the weight of evidence (see text for details) simply that the ordinate. The two insets illustrate the correspondence between the weight
1
to make of evidencepressedrule:antineuronscales i rearranges as hypothetical (normal, equivariate) probability(8)
Decision neuron and the distributions of theattotal number of spikesBgenerated by the neuron and anti...
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This note was uploaded on 09/15/2011 for the course COGS 1 taught by Professor Lewis during the Spring '08 term at UCSD.
 Spring '08
 LEWIS

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